Behringer UCA202 / UCA222 USB Soundcard headphone improvement

This hack, for the Behringer UCA202 / UCA222 turns an already very good, and very cheap, USB Soundcard into a truly fabulous headphone driver. It improves the sound quality markedly on my low impedance headphones and, although this is a feature I did not need at all, increases the maximum atainable volume of your headphones.

For headphone with less than 50ohm, you only need to replace two SMD resistor and two through-hole capacitors. For headphones with higher impedance, you may want to replace the opamp too.

I am really impressed with the end result of this modification. The geezer that deserves all the credit for this mod is the "Northwest Audio & Video Guy". If your into audio or analog electronics, then you'll love his blog. Well, it's more an encyclopediog, than a blog, going by the size of his articles. Great stuff. Here's the article describing this particular hack in the deepest possible detail:

http://nwavguy.blogspot.com/2011/03/behringer-uca202-frankendac.html

An excerpt From the creator's blog:

"Behringer likely designed the UCA202's headphone jack for use with higher impedance studio headphones. While it can drive such phones fairly well, it's not very compatible with typical consumer 16 - 32 ohm headphones. (...) The new amp can much better drive lower impedances at low distortion and generate much more output power from the same power supply voltage. A few other component changes were also required to optimize the new design. (...) Using Ultimate Ear's headphones, the frequency response improved from +/- 7 dB to a much more neutral +/- 1 dB. (...) The modified Behringer UCA202 has enough power to satisfy most anyone (...) And the output impedance drops from a very poor 50 ohms to only 2.5 ohms. It retains its previously low distortion, similar noise levels, and most other characteristics."

Required:

- ESD protection gear (if you don't use it, you might fry your hardware)
- SMD soldering skills (mostly if you are going to replace the opamp)
- fine-tipped soldering iron
- solder
- flux (cheap resin-based flux is fine)
- optional: solder wick
- optional: (cheap) multi meter
- A vice or something else to hold the PCB while working on it
- Philips screwdriver
- Needle-nose pliers
- optional: fine wire cutter

- optional: 1x opamp AD8656 in SOIC package, costs about 3.30 euro a piece or 2.37 per 10 euro at Farnell
- 2x 6v3 / 2200uf (I used 1600uF, as that was what I had laying around.)
- 2x 2.2ohm / 1% 0806 SMD resistors

NOTE 1: The Behringer UCA 202 hardware seems to be 100% identical to that of the UCA 222. The only difference is the color of the housing.

NOTE 2: I used the SOIC package version of the OPAMP. The MSOP package may be better fit, but is cost 50% more than the SOIC package, so I just went with the SOIC.

NOTE 3: The original article mentions optionally using the possibly better performing opamp AD8397. I did not choose to try that option because it was more expensive, untested and the results of using the less expensive AD8656 are more than satisfactory for me.

Step 1 Open it up

Open up the casing by remove the two philips screws and place the PCB in a vice or something else to keep it in place.

NOTE: At this point it would be wise to get your ESD protection gear out and use it.